The present invention relates to a pattern formation method for forming a resist pattern by selectively irradiating a resist film made from a chemically amplified resist material with extreme UV or an electron beam.
In processes for semiconductor integrated circuit devices, lithography technique is desired to be further developed in accordance with increase of the degree of integration and downsizing of semiconductor integrated circuits.
As exposing light employed in the lithography technique, a mercury lamp, KrF excimer laser (of a wavelength of a 248 nm band), ArF excimer laser (of a wavelength of a 193 nm band) or the like is currently used. For the generation of 0.1 μm or less, and particularly of 0.05 μm or less, whole exposure to extreme UV of a wavelength (of a 1 nm through 30 nm band) shorter than that of the ArF excimer laser or an electron beam (EB) is now being examined to be employed.
In the lithography technique using extreme UV or an electron beam as the exposing light, a chemically amplified resist material with high resolution and high sensitivity is preferably used.
Therefore, in the lithography technique using extreme UV or an electron beam, a chemically amplified resist material suitable for the ArF excimer laser lasing at a wavelength close to that of extreme UV is now being examined for use.
Now, a first conventional pattern formation method will be described with reference to FIGS. 3A through 3D.
First, a chemically amplified resist material having the following composition is prepared:
Base polymer: poly((t-butyloxystyrene) − (hydroxystyrene))1.8 g(wherein t-butyloxystyrene:hydroxystyrene = 40 mol %:60 mol %)Acid generator: triphenylsulfonium triflate0.4 gSolvent: propylene glycol monomethyl ether acetate20 g
Next, as shown in FIG. 3A, the chemically amplified resist material having the aforementioned composition is applied on a semiconductor substrate 1 so as to form a resist film 2 with a thickness of 0.2 μm.
Then, as shown in FIG. 3B, the resist film 2 is selectively irradiated for pattern exposure with extreme UV 3 (of a wavelength of a 13.5 nm band) with exposure energy of 30 MJ/cm2 through a reflection mask (not shown) having a desired mask pattern. After the pattern exposure, as shown in FIG. 3C, the resist film 2 is subjected to post-exposure bake (PEB) with a hot plate at a temperature of 100° C. for 60 seconds.
In this manner, an exposed portion 2a of the resist film 2 becomes soluble in an alkaline developer owing to a function of an acid generated from the acid generator while an unexposed portion 2b of the resist film 2 remains insoluble in an alkaline developer because no acid is generated from the acid generator therein.
Next, the resist film 2 is developed with an alkaline developer, such as a 2.38 wt % tetramethylammonium hydroxide developer, so as to form a resist pattern 4 with a line width of 0.07 μm from the unexposed portion 2b of the resist film 2 as shown in FIG. 3D.
Next, a second conventional pattern formation method will be described with reference to FIGS. 4A through 4D.
First, a chemically amplified resist material having the following composition is prepared:
Base polymer: poly((t-butyloxycarbonyloxystyrene) − (hydroxy-1.8 gstyrene)) (wherein t-butyloxycarbonyloxystyrene:hydroxystyrene =35 mol %:65 mol %)Acid generator: triphenylsulfonium triflate0.8 gSolvent: propylene glycol monomethyl ether acetate20 g
Next, as shown in FIG. 4A, the chemically amplified resist material having the aforementioned composition is applied on a semiconductor substrate 1 so as to form a resist film 2 with a thickness of 0.2 μm.
Then, as shown in FIG. 4B, the resist film 2 is selectively irradiated for pattern exposure with an electron beam (of 100 kV) with exposure energy of 25 μC/cm2 through a mask 6 having a desired mask pattern. After the pattern exposure, as shown in FIG. 4C, the resist film 2 is subjected to post-exposure bake (PEB) with a hot plate at a temperature of 110° C. for 60 seconds.
In this manner, an exposed portion 2a of the resist film 2 becomes soluble in an alkaline developer owing to a function of an acid generated from the acid generator while an unexposed portion 2b of the resist film 2 remains insoruble in an alkaline developer because no acid is generated from the acid generator therein.
Next, the resist film 2 is developed with an alkaline developer, such as a 2.38 wt % tetramethylammonium hydroxide developer, so as to form a resist pattern 4 with a line width of 0.06 μm from the unexposed portion 2b of the resist film 2 as shown in FIG. 4D.
The exposure energy of the extreme UV is 30 mJ/cm2 in the first conventional method and the exposure energy of the electron beam is 25 μC/cm2 in the second conventional method. Thus, large exposure energy is required in any of the conventional methods. This is because a conventional chemically amplified resist material is not sufficiently sensitive to extreme UV or an electron beam.
Since large exposure energy is thus necessary in the conventional pattern formation method using extreme UV or an electron beam as the exposing light, the throughput in the lithography in the semiconductor fabrication process is disadvantageously poor.
Although the exposure energy of extreme UV or an electron beam can be lowered by increasing the amount of the acid generator included in the chemically amplified resist material, when the amount of acid generator is increased, particles are unavoidably produced in the chemically amplified resist material. Therefore, the amount increase of the acid generator is not preferred.